The invention relates to metal forming, and more particularly to a method of rolling section billets.
The invention may be utilized where continuous casting machines are used in combination with a rolling mill in the manufacture of section billets of ferrous or non-ferrous metals. The invention may also be used in roughing stands of section and wire mills and in continuous billet rolling mills.
In the majority of industrially developed countries in the world, there is a permanent shortage of finished section rolled stock which is manufactured of section billets. This is due, on the one hand, to the development from metal consuming industries, and on the other hand, to insufficient output of rolling mills manufacturing section billets. Constant demand for section billets requires an increase in the output of reducing and billet rolling mills. Therefore, a problem arises of providing new manufacturing processes for the production of section billets.
Such manufacturing processes should, first, reduce the production cost of the rolling; second, improve the output of rolling mills; and third, enable a combination of a continuous casting machine and a reducing mill in a single production line.
A conventional production system presently employed for rolling section billets comprises: an ingot-blooming-continuous billet rolling mill. However, all known methods of improving the output of section billets using this production system have reached their limit. An important disadvantage of the conventional system resides in a large metal consumption rate.
In industrially developed countries, up to 20% of the total volume of steel produced is manufactured by continuous casting methods. However, low casting, speeds and hence low productivity, as well as non-uniformity of metal properties over the cross-section and the length of the ingot hamper the production of section billets in continuous casting machines.
Known in the art is a method of making billets, in which a slab having a high width-to-height ratio is produced in a continuous metal casting plant. After complete solidification, the slab is cut apart transversely by using gas cutting torches into individual billets, thereby eliminating reducing and billet rolling.
This method has, however, a number of disadvantages including a large metal consumption rate due to metal losses in gas cutting, and also the billets are of poor quality due to the phase separation on the surface upon transversely cutting the slab.
Also known in the art is a method of splitting triple billets by rolling them between rolls having relatively eccentrical grooves cut along a helical line.
This method involves practical difficulties due to the problems arising in cutting grooves and installing fittings. In addition, the application of this method is limited to the separation of no more and no less than three billets.
Another known process is a method of continuously making section billets comprising subjecting a continuous slab leaving a mould to a successive reduction between a series of cailbrated rolls until complete solidification. As a result of deformation of the wider sides, the slab takes a shape of a plurality of interconnected square billets. After secondary cooling with sprayed water, the billets are cut lengthwise and transversely to obtain measure lengths.
One of the disadvantages of this method resides in low quality of separation zones when using thermal cutting or cutting with circular saws, and where gas cutting is used, metal consumption increases.
Known in the art is a method of making twin billets, in which a continuously cast rectangular-section slab is rolled between a number of twin grooves arranged in series, the cross-sectional shape of the grooves gradually approximating a square or rhombus. The resultant billets are then cut apart by means of gas cutters.
This method is closer in its concept to the conventional rolling in cut grooves, however, the method of cutting is uneconomical due to considerable metal consumption.
It is also known to manufacture section products by the rolling of wide billets in transversely juxtaposed grooves. As a result of billet reduction, a multiple billet is formed which consists of two or more section billets interconnected by bridges of reduced section. The section billets are separated from one another by causing a vertical displacement of the section billets relative to one another. The separation may be effected in both the hot and cold state.
The known method also has disadvantages, and most important among them is low quality of portions of the billets adjacent to cutting zones due to the presence of burrs.
It is an object of the invention to eliminate the abovementioned disadvantages.
Still another object of the invention is to provide a method of rolling which not only increases the output of rolling mills in the manufacture of section billets, but also utilizes a continuous metal casting machine and a reduction mill as an integral production unit. The method of the invention also reduces production cost of the section billets, facilitates automation of the rolling mill and improves quality of the billets.
These and other objects are accomplished by a method of rolling section billets comprising successively forming billets of a slab in a number of grooves defined by a plurality of transversely juxtaposed grooves, the billets being transversely interconnected by bridges, and separating the billets from one another, when the thickness of the bridge becomes equal to 0.01-0.3 of the groove height. The adjacent billets are displaced relative to one another by acting with the groove prevailingly on one of the sides of the adjacent billets at angle other than 90.degree. to the roll axis.
Using this method, section billets having a high surface quality may be produced, the output of rolling mills is improved, and the production cost of section billets is reduced.
In accordance with one embodiment of the invention, at least one more displacement of the billets is effected in the direction opposite to the initial displacement.
This facility improves quality of section billets in the zones of their separation from one another since there are no burrs, and the angles at vertexes of the billets are rounded.
The relative displacement of adjacent billets is preferably effected in a direction at right angle to the reduced sides; and the adjoining portions of the adjacent billets which are formed by juxtaposition of sides of the adjacent billets and define bridges, serve as pilot surfaces for displacement.
This facility provides for high-quality separation of billets from one another and eliminates metal losses for bridges.
In accordance with another embodiment of the invention, the billets may be displaced relative to one another also in the direction of their longitudinal axes.
This enables a reduction in the number of passes required to separate the billets from one another, which is an improvement in the output of rolling mills; and quality of the separation zones of the billets is also enhanced.
Still another embodiment of the invention resides in the fact that the amount of relative displacement of adjacent billets is increased for the billets remote from the middle of the groove.
Thus, billets can be separated from one another in a single pass so that the total rolling cycle is reduced, and output of the rolling mills improved.
Further embodiments of the invention involve a simultaneous displacement of several adjacent billets by one the same amount before the relative displacement of adjacent billets.
This facility permits the billets to be separated from one another in a maximum of two passes. Yet another embodiment of the invention resides in that the direction of prevailing action with the groove on the sides of the billets located on different sides of the middle of the groove intersect at an angle of 90.degree..
This succession of steps enables the elimination of axial forces in the groove, thereby improving the accuracy of the billets being produced and enhancing the gripping conditions.